I've been using Photoshop for over 15 years and am I guess what you would call an expert. However, I do have an embarrassing secret--I never took the time to learn Illustrator! There have been some days where I wish I knew how to use it, but I have been able to get by with Photoshop.
Honestly, should I take the time to learn Illustrator now or do you all think that Photoshop is really all that is needed? With Photoshop's SMART OBJECT feature (Smart Objects preserve an image’s source content with all its original characteristics, enabling you to perform nondestructive editing to the layer), vector text and shapes, robust pen tool, and today's high resolution computer monitors (now you can truly edit your stuff at 300-600dpi for scalability), is there any good reason to learn Illustrator?
I do, admit, that for logo design it seems Illustrator would be beneficial due to the brushs, but again, one can get by nicely with just Photoshop.